1. Field of the Invention
This invention relates to the preparation of asphaltic compositions useful for making paving formulations. These compositions are made by combining certain asphalt fractions, such as asphaltenes and/or residual pitches (which were heretofore thought to be unsuitable for making paving formulations), with propane precipitated asphalt and/or petrolene fractions. The latter components, which must have a polar content of at least 20%, render the total composition sufficiently homogeneous to be useful in paving formulations.
2. Description of the Prior Art
It is well known that certain asphalt fractions cannot be used for formulation of paving binders because of their inhomogeneity as reflected by a positive response to the Oliensis Spot Test (AASHO Test Designation T-102-57). Such fractions are called "positive spot" asphalt fractions and have usually been diverted into relatively uneconomical uses such as for fuel.
It has been known in the prior art that asphalts suitable for use in paving formulations can be prepared by various techniques such as (a) blending residua from two or more crude sources, (b) reconstituting an asphalt from its components (see, e.g., British Specification No. 465,288) or (c) air-blowing asphaltic fractions containing synthetic polymers (see, e.g., U.S. Pat. No. 3,540,906). Still, the need for efficient, economical techniques for allowing the use of positive spot asphalt fractions in paving formulations has not been fully met.
It is an advantage of the present invention that positive spot asphalt fractions, which of themselves have little value beyond their value as fuels, can be included in compositions suitable for use in paving formulations.